How can all four men cross the bridge in 17 minutes?

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Four men want to cross a bridge. They all begin on the same side. It is night and they have only one flashlight with them. At most two men can cross the bridge at a time and any party who crosses, either one or two people, must have the flashlight with them. The flashlight must be walked back and forth: it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the speed of the slower man. Man 1 needs 1 minute to cross the bridge, man 2 needs 2 minutes, man 3 needs 5 minutes, and man 4 needs 10 minutes. For example, if man 1 and man 3 walk across together, they need 5 minutes.

How can all four men cross the bridge in 17 minutes?

posted May 8, 2014

First Man 1 & Man 2 will cross so 2mints
then Man 1 returns so 1mint
then Man 10 & Man 5 will cross so 10mints
then Man 2 returns so 2mints
finally Man 1 & Man 2 will cross so 2mints

Thus total time taken ( 2+1+10+2+2)17mints

+1 vote

MAN 1 AND MAN2 CROSS =2MIN
MAN 1 RETURN=1MIN
MAN 3 AND MAN 4 CROSS =10MIN
MAN 2 RETURN=2MIN
MAN1 AND MAN2 CROSS=2MIN

answer Jun 23, 2014 by anonymous
+1 vote

A and B cross first using up 2 minutes.
A comes back making it 3
C and D cross making it 13 minutes
then B crosses back over making it 15 minutes.
And finally A and B cross together to make it 17 minutes.

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